1. Field of the Invention
The present invention relates to a warning system for a vehicle, for assisting the driver in safety driving and, more specifically, to a warning system for preventing the driver from falling into a doze while driving a vehicle, avoiding collision and preventing swerving of the vehicle from their lane without driver's intention.
2. Description of the Related Art
Recently, an ADA system (Active Drive Assist system), i.e., a comprehensive driver assisting system for actively assisting the driver in driving a vehicle, has been developed in an attempt to enhance the safety of vehicles to cope with progressively increasing traffic accidents. The recognition of the environments of the vehicle is an essential function of the ADA system. Recent advanced technology has made possible the three-dimensional recognition of road conditions and traffic conditions in a practically effective accuracy and time by processing image information about a scene lying ahead of the vehicle acquired by a plurality of cameras. The ADA system is intended to assist the driver in safety driving in many respects by using image data on road conditions and traffic conditions when the driver fails in correct driving operations, when the driver looks aside and/or when the driver dozes off during monotonous driving.
A previously proposed drive assistance system is based on a conception that every operation of a vehicle is to be controlled by a man and intends preventive security for avoiding expected dangers. The drive assistance system gives a warning to warn the driver against an expected danger to assist the driver in safety driving when a car collision or off-course travel is expected and, if the driver does not take appropriate measures to avoid danger in response to the warning, carries out operations temporarily for the driver to avoid a car collision or off-course travel by automatically controlling the brake system, the throttle and/or the steering system to return the traveling condition of the vehicle to safety.
The warning provided by the ADA system would be very useful for the driver to estimate various possible incidents and for enhancing preventive security. Therefore, it is necessary to give a warning properly to enable the driver to take danger avoiding measures by deciding the situation and accurately estimating possible incidents, effectively using image data.
Driver's dozing during driving due to the declination of wakefulness is one of the possible incidents. Roads on which vehicles travel are classified roughly into open roads and automobile roads, such as freeways and superhighways. Since open roads are used by both vehicles and pedestrians and traffic signals are installed on open roads, the driver needs to perform frequently driving operations for starting, accelerating, stopping, turning along sharp curves and such, and is required to pay attention continuously to pedestrians for safety driving. Therefore, the driver is prevented from falling into a doze by continuous stimulation during driving on open roads and hence driver's wakefulness is maintained necessarily on a high level. Generally, driver's wakefulness declines during extended travel in a monotonous traveling mode in which driver's frequent driving operations are unnecessary. Traffic conditions of automobile roads, differing from those on open roads, force the driver to perform long, monotonous driving operations and, consequently, driver's wakefulness declines and the driver is liable to fall into a doze. However, driver's wakefulness is maintained on a high level even if the vehicle travels on a long, straight road requiring only a few driving operations when even only one of psychological stimuli, such as a stimulus received from another vehicle overtaking the vehicle or cutting into the way of the vehicle and a stimulus received from a narrow lane, and visual stimuli is provided to the driver. Accordingly, it is desirable to determine the degree of driver's wakefulness through the detection of visible matters that provide psychological stimuli to the driver and to give the driver a warning against dozing. It is necessary to determine whether the vehicle is traveling on an automobile road or an open road and to watch the driver for dozing particularly when the vehicle travels on an automobile road.
As is generally known, dozed men's driving has a high possibility of causing collision against the preceding vehicle or off-lane travel. Therefore, it is desirable to warn the driver for preventive security at an early stage to prevent driver's doze off when driver's wakefulness is on a low level and car collision and off-lane travel is expected.
A first prior art doze warning system disclosed in JP-B No. 59-16968 sets a fixed road section, decides that the road section is a monotonous one when the number of operations executed in the road section is not greater than a set number, and provides awakening alarm when the number of successive monotonous road sections exceeds a reference number. A second prior art doze warning system disclosed in JP-B No. 59-16969 decides the vehicle is traveling in a monotonous traveling mode when the frequency of variation of the angular position of the steering wheel or the operating position of the accelerator is less than a set frequency. A third prior art doze warning system disclosed in JP-B No. 61-53250 detects an environment that will possibly lower the level of driver's senses on the basis of the mode of steering operation, accumulates steering angles through which the steering wheel were turned in the environment, decides the condition of the road on the basis of the cumulative steering angle, decides that the condition of the road is monotonous and gives a warning when the cumulative steering angle is less than a set value.
A fourth prior art doze warning system disclosed in JP-A No. 5-162596 determines safety car-to-car distances for traveling speeds beforehand, decides that collision is possible when the current car-to-car distance is less than a safety car-to-car distance for the traveling speed of the vehicle and gives a warning. The timing of giving a warning is adjusted according to the level of driver's senses evaluated on the basis of the means and the standard deviations of car-to-car distances when the brake is applied and car-to-car distances in the normal traveling mode.
Since those prior art doze warning systems detects the monotonous driving mode on the basis of the driver's steering pattern or accelerator operating pattern and gives a warning depending on the condition of the road, and are unable to detect the degree of driver's wakefulness dependent on psychological stimuli, those prior art doze warning systems give an unnecessary warning frequently. Although the level of driver's senses on the basis of which the timing of giving a warning is adjusted is evaluated on the basis of the car-to-car distance at which the brake is operated, the mode of operation of the brake is dependent on traffic conditions and is not a suitable standard for the evaluation of the level of driver's senses.
A fifth prior art dozed driving detecting system disclosed in JP-A No. 5-155269 uses a fact that steering angle varies slowly and low frequency components increase when driver's senses decline for detecting dozed driving. This dozed driving detecting system determines a characteristic frequency peculiar to the driver from the frequency spectrum indicating the movements of the vehicle in the normal traveling mode, extracts a low-frequency component of a frequency lower than the characteristic frequency at predetermined time after the start of driving operation by a predetermined value, and determines whether or not the driver is in dozed driving on the basis of the result of comparison between the low-frequency component and a set threshold.
A sixth prior art dozed driving detecting system disclosed in JP-A No. 5-178115 uses a fact that the driver becomes aware of an abnormal transverse deviation of the vehicle with a delay and needs a comparatively long time for correcting the traveling course of the vehicle when the driver's senses are lowered. This dozed driving detecting system calculates a reference position, i.e., a position of the vehicle in the normal traveling mode, measures the returning time spent to return the vehicle from a displaced position to the reference position when the vehicle is displaced from the reference position at time after the start of traveling, and decides whether or not the driver is in dozed driving on the basis of the result of comparison between the returning time and a given time.
The fifth and sixth prior art dozed driving detecting system do not discriminate between open roads and automobile roads and hence the following problems resides in those dozed driving detecting systems. Generally, open roads have comparatively narrow lanes, there are pedestrians and parking cars and bicycles on the edge sections of open roads, vehicles traveling near and on the opposite sides of the center line travel in opposite directions, and vehicles travel at comparatively low traveling speeds in the central sections near the center line or in the outer sections of roads. On the other hand, automobile roads have wide lanes and vehicles travel rapidly through the substantially central section of wide lanes. Therefore, the traveling pattern of vehicles and the pattern of driver's driving operation on automobile roads are greatly different from those on open roads. Accordingly, driver's doze cannot be accurately detected when the reference traveling pattern of the vehicle and the reference position of the vehicle determined on the basis of traffic conditions of open roads are applied to detecting driver's doze when the driver is driving the vehicle on automobile roads.